Recently, OLEDs have become appropriate mediums for displaying high-resolution moving images because they consume little power and have high luminous efficiency, wide viewing angles, and fast response speeds. For these reasons, OLEDs have attracted much attention as next-generation displays.
A typical OLED includes an organic emission layer positioned between an anode and a cathode. The OLED is a self-emissive display in which voltage is applied between the anode and the cathode, causing electrons to recombine with holes in the organic emission layer, thereby generating light. Since the OLED does not require a backlight such as a liquid crystal display (LCD), it may be lightweight and thin and fabricated by a simple process.
OLEDs may be classified into small molecular OLEDs and polymer OLEDs according to the material of the organic emission layer.
A small molecular OLED includes a multilayered organic layer having different functions. For example, the organic layer may include a hole injection layer, a hole transport layer, an emission layer, a hole blocking layer, and an electron injection layer, each positioned between an anode and a cathode. To prevent accumulation of charges, the organic layer may be doped or may comprise a material having an appropriate energy level. However, these organic layers are typically formed by vacuum deposition, making it difficult to fabricate larger displays.
A polymer OLED can include either a single organic emission layer or a double-layered structure including an organic emission layer and a hole transport layer. Thus, polymer OLEDs may be fabricated with smaller thicknesses. Also, because the organic layer is formed by wet coating, it may be formed under normal pressure, thereby greatly reducing production cost and enabling easy manufacture of larger OLEDs.
Polymer OLEDs are easily fabricated by spin coating, but are inferior in efficiency and lifetime than small molecular OLEDs. Also, full-color devices may be fabricated by patterning red (R), green (G), and blue (B) emission layers on OLEDs. An organic layer of a small molecular OLED may be patterned by deposition using a shadow mask. An organic layer of a polymer OLED may be patterned by inkjet printing or laser induced thermal imaging (LITI). Since LITI uses spin coating features, larger organic layers are formed and pixel uniformity may be improved. Also, because LITI is a dry process, reduction in the lifetime of the OLED that can occur with solvents is prevented and the organic layer may be finely patterned.
LITI basically requires a light source, an OLED substrate and a donor substrate. The donor substrate includes a base layer, a light-to-heat conversion (LTHC) layer and a transfer layer.
During LITI, light is emitted from the light source and absorbed in the LTHC layer, thus converting the light into thermal energy and forming an organic material on the transfer layer which may be transferred onto the substrate by the thermal energy.
Methods of patterning an organic layer on an OLED using LITI are disclosed in Korean Patent Registration No. 10-0342653 and U.S. Pat. Nos. 5,998,085, 6,214,520 and 6,114,085.
FIGS. 1A through 1C are cross-sectional views of a prior art method of patterning an organic layer 23 using LITI.
As shown in FIG. 1A, a substrate 10 and a donor substrate 20 including a base layer 21 are provided. An LTHC layer 22 and an organic layer 23 are laminated on the substrate 10.
As shown in FIG. 1B, laser beams are irradiated onto the base layer 21 of the donor substrate 20 in a first region a. The laser beams are transmitted through the base layer 21 and converted into heat in the LTHC layer 22. The heat weakens the adhesion of the organic layer 23 with the LTHC layer in the first region a.
As shown in FIG. 1C, after the organic layer 23 in the first region a is transferred to the substrate 10, the donor substrate 20 is detached from the substrate 10. Thus, an organic transfer layer 23a is patterned on the substrate 10, and an organic layer 23b in a second region b is detached from the substrate 10 along with the donor substrate 20, thereby completing the organic transfer pattern 23a. The second region b is the region to which no laser beams are irradiated.
However, in forming the organic transfer layer 23a by LITI, static electricity may be generated from rubbing and other external environmental factors that may occur during the attachment/detachment of the donor substrate 20 to/from the substrate 10. Since voltage can reach several thousands to several tens of thousands during discharge, the static electricity may cause a short circuit at a junction of the OLED, the metal layer may melt due to a rise in the temperature of the OLED, or a junction line may open. If such failures occur in the OLED, the internal circuit of the OLED may be adversely affected, thereby deteriorating the properties of the OLED.